The Madden-Julian oscillation (MJO), the dominant source of Earth system predictability at the intraseasonal time scale, is a known driver of many types of extreme events all over the globe. Unfortunately, however, an accurate representation of the MJO and its teleconnections is still one of the most challenging tasks for many global climate models (GCMs). The goal of the present study is to thoroughly examine the characteristics of the MJO represented in the Energy Exascale Earth System Model version 1 (E3SM), DOE’s new Earth system model. Simulations made with E3SM are analyzed in terms of the MJO moist static energy (MSE) budget and relevant mean state, the interaction of MJO with the maritime continent (MC) islands, MJO teleconnections to the mid-latitudes, as well as the interannual variability of the MJO. Processes that have been suggested as critical to MJO simulation are examined by utilizing recently developed process-oriented diagnostics.
E3SMv1 realistically represents the eastward propagation of precipitation and MSE anomalies associated with the MJO. As in observations, horizontal moisture advection and longwave radiative feedback are found to be the dominant processes that lead to the eastward movement and maintenance of MSE anomalies in the model, respectively. The modulation of the diurnal cycle of precipitation in the MC region by the MJO is also well represented despite systematic biases in the magnitude and phase of the diurnal cycle. E3SMv1 also reasonably captures the pattern of the MJO teleconnection, with improvement in the performance in a high-resolution version, while the magnitude is a bit weaker than the observed.
It is found that the El Nino-Southern Oscillation (ENSO) affects the zonal extent of MJO’s eastward propagation via the mean state moisture gradient in the tropical west Pacific. Compared to La Nina years, an El Nino year features a weaker negative zonal moisture gradient and a stronger positive meridional gradient, both facilitating further eastward propagation of MJO. However, like many other contemporary GCMs, MJO in E3SM exhibits no sensitivity to the Quasi-Biennial Oscillation (QBO), with the MJO propagation characteristics being almost identical between easterly QBO and westerly QBO years.